[PATCH 6/6] riscv: enable DMA_BOUNCE_UNALIGNED_KMALLOC for !dma_coherent

[Jisheng Zhang]

With the DMA bouncing of unaligned kmalloc() buffers now in place,
enable it for riscv when RISCV_DMA_NONCOHERENT=y to allow the
kmalloc-{8,16,32,96} caches. Since RV32 doesn't enable SWIOTLB
yet, and I didn't see any dma noncoherent RV32 platforms in the
mainline, so skip RV32 now by only enabling
DMA_BOUNCE_UNALIGNED_KMALLOC if SWIOTLB is available. Once we see
such requirement on RV32, we can enable it then.

NOTE: we didn't force to create the swiotlb buffer even when the
end of RAM is within the 32-bit physical address range. That's to
say:
For RV64 with > 4GB memory, the feature is enabled.
For RV64 with <= 4GB memory, the feature isn't enabled by default. We
rely on users to pass "swiotlb=mmnn,force" where mmnn is the Number of
I/O TLB slabs, see kernel-parameters.txt for details.

Tested on Sipeed Lichee Pi 4A with 8GB DDR and Sipeed M1S BL808 Dock
board.

Signed-off-by: Jisheng Zhang <jszhang@xxxxxxxxxx>
---
 arch/riscv/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index b958f67f9a12..14f030cd6357 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -260,6 +260,7 @@ config RISCV_DMA_NONCOHERENT
 	select ARCH_HAS_SYNC_DMA_FOR_CPU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE
 	select DMA_DIRECT_REMAP
+	select DMA_BOUNCE_UNALIGNED_KMALLOC if SWIOTLB
 
 config AS_HAS_INSN
 	def_bool $(as-instr,.insn r 51$(comma) 0$(comma) 0$(comma) t0$(comma) t0$(comma) zero)
-- 
2.40.1